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\fancyhead[L]{P2P project activity}
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\author{Nick Lauritsen\\20061459}
\title{P2P project activity}
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\begin{abstract}
\end{abstract}

\section{Motivation}

\section{Related work} \label{related_work}
\textbf{Workshop on Economics of Peer-to-Peer systems} - 2003

\textbf{Dissecting bittorrent: Five months in a torrent's lifetime} - 2004 x

\textbf{BASS} - 2006 x

\textbf{Understanding user behavior in large-scale video-on-demand systems} - 2006

\textbf{BiToS} - 2007 x

\textbf{Is high-quality VOD feasible using P2P swarming?} - 2007 x

\textbf{Peer-to-peer multimedia streaming using BitTorrent} - 2007

\textbf{Challenges, design and analysis of a large-scale p2p-vod system} - 2008

\textbf{Watch Global, Cache Local: YouTube Network Traffic at a Campus Network - Measurements and Implications} - 2008

\textbf{Windowing BitTorrent for Video-on-Demand: Not All is Lost with Tit-for-Tat} - 2008

Bittorrent is a P2P application that capitalizes the resources, e.g. access bandwidth and disk storage, of peer nodes to distribute large contents \cite{Izal:2004sp}. The single objective of bittorrent is to quickly replicate a single large file to a set of clients, meaning that bittorrents goal is to maximize the speed of this replication. This speed relies among other things on the chunk picking strategy implemented by the different peers, which in a bittorrent client, following the bittorrent protocol, is rarest-first.
The rarest-first chunk picking strategy is however not suited for VoD services, since the different chunks are not requested in an order which makes it possible to start viewing a video before a download has ended. To handle this \cite{dana2006bass} proposed a novel streaming system called BitTorrent Assisted Streaming System, in short BASS, for VoD services, where the use of an external streaming server is added to a slightly modified BitTorrent system. It is important to notice that simply forcing the bittorrent system to request chunks sequentially would have disasterous results because then clients would only contain subsets of each others data and tit-for-tat would fail \cite{dana2006bass}. BASS uses an external media server with the only modification to BitTorrent being that it does not download any data prior to the current playback point. It is allowed to use the rarest-first and tit-for-tat policies, as long as it is before the current playback point.

\cite{vlavianos2007bitos} describes a so-called "view-as-you-download service" based on bittorrent. The algorithm used in this article is based on three sets, the first being a set containing the recieved chunks, meaning it contains all chunks which the current peer has dowloaded for the current torrent. The second set being a high priority set, meaning a set containing all the chunks which the player needs in the nearest future. The last an third set is a set containing all remaining chunks, meaning all the chunks which have not yet been downloaded and have not yet been added to the high priority set. Notice that the different chunks in the high priority set are downloaded using the rarest-first algorithm.

The reason that the rarest-first algorithm is used within the high priority set is to utilize as many system ressources as possible. This notion of system utilization in VoD services is furthermore explored in \cite{annapureddy2007high}, where different algorithms are explored with regards to their throughput (system utilization) and their goodput (videos viewability). It is observed that the algorithm which provides the best throughput and goodput is an algorithm which splits a file up into segment each containing a number of chunks. Two segments are picked using heuristics, such as where in the video the user is at the current moment. A chunk is now picked using rarest-first strategy in one of these two segments, furthermore the segment to perform rarest-first in is picked using a biased coin where the first segment has a probability of 90 percent and the second a probability of 10 percent.



\section{Hypothesis} \label{sec:hypothesis}

\section{Conclusion}

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